(1) Field of the Invention
The present invention relates to wind power generating devices, specifically to wind wheel style turbines.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
With the current climate change crisis and rising energy demand, the world is looking at wind power to supply a greater share of that energy demand. While wind energy is widely available, it is a dilute form of energy, and wind turbine blades have to be large to generate a sufficient amount of energy from that medium.
Most wind turbines are either of the horizontal or vertical shaft type. Prior vertical shaft turbine designs have proven uneconomic and achieved only limited success. Of the horizontal shaft turbine designs, most either have the blades in a self-supporting cantilever style, or have blades that are supported at their edges by a rim (a wind wheel design). The former is the most common wind turbine technology; it is the horizontal axis upwind 3-bladed design pioneered by Danish companies and used all over the world. As for the latter (wind wheel), while a few patents have been granted on that design, it has never been utilized on a commercial scale.
The disadvantages of the cantilevered blade design are as follows. It has a high center of gravity, as most of the massive components—the heavy steel hub, nacelle, yaw drive, and slew ring—are located on top of the tower. This requires the tower to be highly rigid to resist the swinging action driven by the massive inertia resulting from a heavy mass on top of the tower. Furthermore, since the blades are cantilevered, they need to be strong enough, and fatigue-resistant enough, to resist the high wind loads on a blade that can be as long as 60 m or even more. Also, because the generator has to rotate at 1500-1800 rpm, and there are economic and practical limits for the gearbox ratio used, there is a certain minimum rotational speed for the rotor blades. Usually, that speed is about 18 rpm for an 80 m diameter turbine, resulting in a fairly high tip speed (around 70 m/s) and high frictional losses to the air. Additionally, the resultant angle of attack between the blade and the wind is very shallow at this tip velocity, which reduces the generated rotational force component. Finally, because these are upwind rotors, they require an extremely strong and precise yaw ring and ring drive—these are usually two or four opposite yaw drive gears that rotate the giant nacelle/rotor, countering tremendous gyroscopic forces. Once the turbine is properly directed facing the wind, the opposing yaw drives lock against each other to take up any backlash in the slew ring gears. Due to these factors and complications, the yaw drive and slew ring system cost is a considerable portion of the total cost of a large wind turbine generator. Similarly, the high bending moment of the cantilevered blades requires a precise and expensive yaw system for each individual blade.
As for the wind wheel design, several patents exist, but none of those designs have proven to be commercially successful. U.S. App. No. 2007/016,6159 to Williams had no means of orienting the turbine to face the wind, and is a low height design confined to the ground, which reduces the amount of wind energy it can catch. U.S. App. No. 2006/027,5121 to Merswolke uses a complicated upwind design, and requires two separate yaw systems—one for the rotor and one for the power takeoff carriage mechanism, which is ground supported, which also limits the height of the design and therefore the amount of wind energy it can catch. U.S. Pat. No. 6,064,123 to Gislason uses a cumbersome ground tracked yawing mechanism, which also confines the operation of the turbine to near the ground. U.S. Pat. No. 4,729,716 to Schmidt uses an upwind configuration and has the same handicaps as Gislason; it also uses a single sail method, which, although cheaper than blades, is seriously aerodynamically inefficient, and uses a complicated blade pitch mechanism. The Schmidt design is also limited to a low height. U.S. Pat. No. 4,350,895 to Cook, like Schmidt, uses aerodynamically inefficient sails, and also has a complicated positive yaw carriage to lift the whole wind wheel and the power takeoff wheels, which also limits the height of the wind wheel. Finally, U.S. Pat. No. 4,319,865 to Richard uses a ground supported carriage to early the power takeoff wheels, which also limits its height. In other words, all of the prior art wind wheels have two limitations—they are limited in their height, which limits the amount of power they can generate, and they have upwind yaw systems, which are cumbersome, heavy, and expensive.